From: Dexuan Cui <decui@xxxxxxxxxxxxx> Sent: Saturday, April 8, 2023 1:48 PM > > When a TDX guest runs on Hyper-V, the UEFI firmware sets the HW_REDUCED > flag, and consequently ttyS0 interrupts can't work. Fix the issue by > overriding x86_init.acpi.reduced_hw_early_init(). > > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> > --- > > Changes since v1: > None. > > arch/x86/kernel/cpu/mshyperv.c | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c > index e9106c9d92f81..deedced0f2bb0 100644 > --- a/arch/x86/kernel/cpu/mshyperv.c > +++ b/arch/x86/kernel/cpu/mshyperv.c > @@ -318,6 +318,26 @@ static void __init hv_smp_prepare_cpus(unsigned int max_cpus) > } > #endif > > +/* > + * When a TDX guest runs on Hyper-V, the firmware sets the HW_REDUCED flag: see > + * acpi_tb_create_local_fadt(). Consequently ttyS0 interrupts can't work because > + * request_irq() -> ... -> irq_to_desc() returns NULL for ttyS0. This happens > + * because mp_config_acpi_legacy_irqs() sees a nr_legacy_irqs() of 0, so it > + * doesn't initialize the array 'mp_irqs[]', and later setup_IO_APIC_irqs() -> > + * find_irq_entry() fails to find the legacy irqs from the array, and hence > + * doesn't create the necessary irq description info. > + * > + * Copy arch/x86/kernel/acpi/boot.c: acpi_generic_reduced_hw_init() but doesn't > + * change 'legacy_pic', so it keeps its default value 'default_legacy_pic' in > + * mp_config_acpi_legacy_irqs(), which sees a non-zero nr_legacy_irqs(), and > + * eventually serial console interrupts can work properly. I had a little trouble parsing this comment. Slightly better wording is: * Clone arch/x86/kernel/acpi/boot.c: acpi_generic_reduced_hw_init() here, * except don't change 'legacy_pic'. It keeps its default value 'default_legacy_pic'. * mp_config_acpi_legacy_irqs() sees a non-zero nr_legacy_irqs(), and * eventually serial console interrupts can work properly. Otherwise, Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> > + */ > +static void __init reduced_hw_init(void) > +{ > + x86_init.timers.timer_init = x86_init_noop; > + x86_init.irqs.pre_vector_init = x86_init_noop; > +} > + > static void __init ms_hyperv_init_platform(void) > { > int hv_max_functions_eax; > @@ -425,6 +445,8 @@ static void __init ms_hyperv_init_platform(void) > > /* A TDX VM must use x2APIC and doesn't use lazy EOI */ > ms_hyperv.hints &= ~HV_X64_APIC_ACCESS_RECOMMENDED; > + > + x86_init.acpi.reduced_hw_early_init = reduced_hw_init; > } > } > > -- > 2.25.1